The present invention relates to dies for extruding honeycomb structures from plasticized organic or inorganic batch materials. More particularly, the invention relates to the discharge face portion of an extrusion die for extruding hexagonal shaped honeycomb structures or cells, and method for producing the such face.
The use of extrusion dies to form thin-walled honeycomb structures is well known in the art. U.S. Pat. Nos. 3,790,654 and 3,905,743 to Bagley describe one design for such a die, with such design incorporating a plurality of feed holes entering an inlet face of a die body, and extending through such body of the die to convey extrudable material to a discharge face section. The outlet face or faceplate area has an array of discharge slots formed about a plurality of pins. The discharge slots, formed between a plurality of such pins interconnect with each other, reforming the extrudable material into an interconnected wall structure for a channeled body as the material is discharged from the outlet face of the die.
The shape of the pins formed in the outlet face of the die determine the shape of the cells formed in the extruded honeycomb structure. The design principles for square, triangular and even hexagonal celled dies are remarkably similar, particularly with regard to the establishment of values for slot depth, hole/slot overlap, feed hole diameter, feeding patterns, knitting zones and other parameters. Moreover, body plates which provide the feed holes for the various cell shapes are essentially alike whether they are of laminated or monolithic construction.
However, the manufacture of an outlet or discharge face portion with hexagonal pins is the most challenging of the three cell designs, because hexagonal slots, formed between the hexagonal pins, do not extend continuously and linearly across the full face of the die. Slots for square and triangular cells are readily formed by tools such as milling saws, abrasive blades and wire-EDM processes, which cut in long straight lines.
Hexagonal faceplates or discharge portions, on the other hand, have slots composed of short segments which join together in a zig-zag fashion and never form a long, straight line across the face of the die. Such non-linear paths do not accommodate tool runout of saws or blades, nor are they compatible with the straight stretched wire configuration of the wire-EDM process. Thus, the present invention is not concerned with the manufacturer of the feed hole portion of extrusion dies, but rather sets forth an improved method for producing a faceplate or discharge face portion for a die capable of extruding hexagonal shaped cells in a honeycomb structure
In the past, hexagonal-celled dies were formed by rather complex and involved time consuming methods such as shown in U.S. Pat. Nos. 5,714,228 and 5,731,562 as well as Japanese Patent Application Disclosure Nos. 63-28523, 63-28522, and 63-28520. The U.S. Patents relate to the creation of a single plunge full-pattern EDM electrode for producing a cellular die. Initially, a plurality of spaced-apart holes are cut through an electrode block, and an electrode wire is positioned through each hole in the block and the wire performs electrical discharge machining to form a cutting surface with a plurality of hexagonal shaped cell walls, and the electrode is then used to EDM cut the faceplate area of an extrusion die.
The Japanese patent application disclosures relate to the manufacture of a honeycomb extrusion die having hexagonal shaped slots for forming an extrusion having hexagonal shaped cells. The die is formed by a plurality of blades which, on their first EDM pass, form opposed slots of a hexagonal configuration. The blades are then rotated 60.degree. and EDM form a second pair of opposed slots of the hexagonal configuration, and finally the blades are again rotated another 60.degree. and produce the final opposed slots of the hexagonal configuration. The methods disclosed in the forgoing U.S. patents and the Japanese application disclosures are cumbersome, expensive and time-consuming.
In light of the known manufacturing difficulties, it is a principal object of the present invention to provide an improved method of producing an extrusion die for extruding honeycomb structures with hexagonal cells.
It is a further object of the invention to provide a method of forming hexagonal shaped pins in the discharge face or faceplate portion of an extrusion die.
Other objects and advantages of the invention will be apparent from the following description thereof.